Denaturation is the process by which foods or liquids are made unpleasant or dangerous to consume; it is done by adding a substance known as a denaturant.
Aversive agents—primarily bitterants and pungent agents—are often used to produce an unpleasant flavor.
[1] A poisonous substance may be added as an even more powerful deterrent.
For example, methanol is blended with ethanol to produce denatured alcohol.
The addition of methanol, which is poisonous, renders denatured alcohol unfit for consumption, as ingesting denatured alcohol may result in serious injury or death.